The invention relates to new photochromic transparent organic materials with a high refractive index, to a process for their preparation, and to the articles made of these materials.
It is difficult to find a photochromic material allowing for the production of an ophthalmic lens whose transmittance varies as a function of the lighting. Outside of their photochromic properties (i.e., colorability, rapid darkening and lightening kinetics, acceptable durability, etc.), such lenses are generally made by the use of appropriate mixtures of photochromic compounds such as spirooxazines and chromenes. The polymer matrixes which are used, though thermally crosslinked, have a low glass transition point, generally lower than that of CR39(copyright), a reference ophthalmic resin consisting of diethylene glycol bis(allyl carbonate) available from PPG Industries, so as to have rapid photochromic kinetics. Moreover, these polymers generally have a relatively low refractive index ( less than 1.54).
The majority of these thermally crosslinked matrixes are obtained by radical polymerization (i.e., polymerization which most often can only be carried out provided that one uses initiators of the organic peroxide type.) The use of organic peroxides makes it practically impossible to incorporate photochromic molecules in the mixture of monomers before polymerization, the peroxides having the effect either of destroying any photochromic effect or of giving the product an unacceptable permanent intense coloration. Also, one is obliged to later incorporate coloring agents into the matrix, most often by a special thermal diffusion process.
Therefore, there continues to be a need for photochromic trans-parent organic materials which have improved photochromic properties and which are easy to manufacture and not very expensive to manufacture.
Briefly, the invention relates to new photo-chromic transparent organic materials which are particularly useful for the production of photochromic organic ophthalmic lenses. The organic material consists of an optical-quality polymer matrix and at least one coloring agent giving photochromic properties to the matrix. The coloring agent is chosen from the group of the spirooxazines, the spiropyrans, and the chromenes. The polymer of the matrix is chosen from (a) homopolymers of ethyoxylated bisphenol A dimethacrylate having formula I: 
in which R is H or CH3, and m and n independently represent 1 or 2, and (b) copolymers of ethoxylated bisphenol A dimethacrylate containing, at most, 30 wt % of at least one aromatic monomer with vinyl, acrylic, or methacrylic functionality.
Surprisingly, we have found that the materials of the invention are characterized particularly by a glass transition point, and therefore by a hardness, which is greater than that of many hitherto known organic ophthalmic products without any adverse effects on the darkening and lightening speeds. We have also found that, through the choice of an appropriate mixture of several coloring agents, it is possible to obtain the desired tint in such matrixes, particularly gray or brown, with this tint practically not varying in the course of darkening and lightening.
The inventive organic materials also exhibit a high refractive index, which is in all cases greater than 1.54, and which can be adjusted, if necessary, to the desired value by the use of an appropriate modifying comonomer.
Useful co-monomers for the invention include vinyl, acrylic or methacrylic compounds containing in their formula one or more benzene nuclei. Examples of some useful co-monomers are, divinylbenzene, diallyl phthalate, benzyl or naphthyl acrylates or methacrylates, etc., as well as their derivatives substituted on the aromatic nucleus or nuclei by chlorine or bromine atoms.
In another aspect, the invention also relates to a process for the preparation of the photochromic organic materials of the invention by polymerizing an ethoxylated bisphenol A dimethacrylate, corresponding to formula I: 
in which R is H or CH3, and m and n independently represent 1 or 2, optionally with up to 30 wt % of one or more modifying aromatic monomers with vinyl, acrylic or methacrylic functionality, in the presence of a diazo radical initiator and in the absence of a peroxide radical initiator. Preferably, R is H, and m=n=2.
Preferably, the polymerization is carried out in the presence of at least one photochromic coloring agent, which allows one to color the final material in its mass.
An essential characteristic of the present process is that it is implemented in the absence of a peroxide radical initiator, the latter being replaced by a diazo initiator. This has the advantage of allowing one to incorporate the photochromic coloring agent in the resin matrix before polymerization of the matrix. Polymerization in the presence of the coloring agent cannot be carried out with a peroxide initiator because the latter may generate a strong initial coloration of the resulting organic glass. The peroxide initiator may also lead to a loss of the photochromic effect. Accordingly, in current processes for the production of organic glasses, when a peroxide initiator is used, a separate coloration step is required in order to re-impart photochromic properties or color back into the glass. As stated earlier, the coloration is generally done for example, by the diffusion of the coloring agent or agents into the glass matrix, usually at elevated temperatures. The preferred inventive process avoids this additional coloring step, and if desired, allows for the production of a photochromic lens in a single step by carrying out the polymerization directly in a lens mold.
Of course, if desired, the coloring agent can be omitted from the polymerizable mixture, and the incorporation of the photochromic coloring agent or agents in the polymerized matrix can be carried out by a conventional thermal diffusion process as described for example, in U.S. Pat. Nos. 5,130,353, 5,185,390 and 5,180,254. According to the method described in these references, a substrate impregnated with photochromic coloring agent or agents is applied to one surface (usually the convex surface in the case of a lens) of the polymer matrix. The impregnated substrate is then heated to 100-150xc2x0 C. for one to three hours, and finally the substrate is separated from the polymer matrix.
The photochromic coloring agent can be chosen from the general classes of the spirooxazines, spiropyrans and chromenes having photochromic properties. Quite a large number of photochromic coloring agents are described in the literature and are commercially available and are described for example in U.S. Pat. Nos. 5,246,630 and 4,994,208, both herein incorporated by reference.
Examples of useful spirooxazines for the invention are described in U.S. Pat. Nos. 3,562,172; 4,634,767; 4,637,698; 4,720,547; 4,756,973; 4,785,097; 4,792,224; 4,784,474; 4,851,471; 4,816,584; 4,831,142; 4,909,963; 4,931,219; 4,936,995; 4,986,934; 5,114,621; 5,139,707; 5,233,038; 4,215,010; 4,342,668; 4,699,473; 4,851,530; 4,913,544; 5,171,636; 5,180,524; and 5,166,345, and also in EP-A 0,508,219; 0,232,295; and 0,171,909, among others, herein incorporated by reference.
Examples of chromenes that can be used are described also in U.S. Pat. Nos. 3,567,605; 4,889,413; 4,931,221; 5,200,116; 5,066,818; 5,244,602; 5,238,981; 5,106,998; 4,980,089; and 5,130,058 and EP-A 0,562,915, all herein incorporated by reference.
Useful spiropyrans have been described in the literature, for example, in Photochromism, G. Brown, Ed., Techniques of Chemistry, Wiley Interscience, Vol. III, 1971, Chapter III, pp. 45-294, R. C. Bertelson; and Photochromism. Molecules and Systems, Edited by H. Dxc3xcrr, H. Bouas-Laurent, Elsevier, 1990, Chapter 8, xe2x80x9cSpiropyrans,xe2x80x9d pp. 314-455, R. Guglielmetti, all herein incorporated by reference.
On an indicative and nonlimiting basis, the proportion of photochromic coloring agent(s) to be incorporated in the matrix can range from 0.03 to 0.3 wt %, and preferably from 0.05 to 0.1 wt %.
Preferably also, one uses a combination of photochromic coloring agents giving a gray or brown tint in the darkened state.
As diazo radical initiator, it is possible to use azobisisobutyronitrile (AIBN) and 2,2xe2x80x2-azobis(2-methylbutyronitrile), among others. Other examples of useful diazo radical initiators are also described in xe2x80x9cPolymer Handbook,xe2x80x9d by Bandrup and Immergut, p. II-2, John Wiley (1989).
To carry out the polymerization, it is possible, for example, to heat the polymerizable mixture slowly until the beginning of thermal degradation of the diazo compound with release of nitrogen and free radicals. This can occur at a relatively low temperature which depends on the diazo compound which is used (approximately 65xc2x0 C. in the case of AIBN). The polymerization is carried out for several hours, for example, 10-20 hours. One finally proceeds to anneal the structure by heating in successive temperature stages, which can exceed 100xc2x0 C., and for a duration of approximately 1 hour each.
The invention finally relates to the articles consisting completely or partially of a photochromic organic material according to the invention.
Nonlimiting examples of such articles are lenses for ophthalmic (corrective) glasses or sunglasses, windows for automobiles and other vehicles, windows for buildings, etc. In the articles of the invention, the photochromic organic material of the invention can constitute the whole thickness of the article (solid article) or can be in the form of a film or layer stratified on a transparent organic or mineral support.
Lenses, especially ophthalmic lenses, are particularly preferred articles of the invention.
These lenses can be produced conveniently by carrying out the polymerization in lens molds, in a conventional manner, for example, as described in U.S. Pat. Nos. 2,242,386; 3,136,000; and 3,881,683 which are herein incorporated by reference.
The stratified articles can be produced easily by application of the polymerizable mixture (for example, by immersion, by centrifugation, by brush, etc.) to the support and polymerization of said mixture in situ.